The present invention relates to initialization and preparation of ultrasonic test stands and equipment for subsequent testing of objects, such as large pipes as to defects, e.g., in welding seams.
Ultrasonic test stands for testing, e.g., the longitudinal or helical welding seam of pipes, require a more or less extensive preparatory procedure before testing proper can begin. First of all, one uses dummies representing the objects expected to be tested. These dummies must have the dimensions as well as ultrasonic transmission and absorption characteristics equal to or in representation of the test objects. The dummy is provided with bores, grooves or the like of well defined dimensions, which are expected to produce particular interference with an ultrasonic probing beam. Since the dummy is actually used for simulation, the type of its grooves, notches, etc., will depend on the type of test, test specifications, etc.
This dummy is used to adjust, position and orient the test heads and their holders generally, whereby particularly parameters such as the distance from the expected welding seam, the sensitivity of test circuitry, the angles of incidence, skip distance, etc., are appropriately adjusted.
The test sensitivity is a particularly critical parameter due to its intimate relation to the response threshold of the test equipment. Proper selection of the grooves, etc., in the dummy for purposes of simulation is, therefore, quite important for the preparation of the equipment.
The known preparation and initialization procedures have posed a variety of problems, and have not yielded satisfactory results. For example, it is difficult to simulate the tolerances in accordance with prescribed test procedures and specifications. This is particularly the case when dummies are prepared to represent pipes or strips.
Another problem is the production of suitable dummies. They are quite expensive to make, e.g., in the case of pipes. It was found that it is actually necessary to use a portion of such a pipe itself. Defects can be simulated only after the dimensions of the section have been determined. Since ultrasonic testing of tubes or pipes in the production line requires incorporation of the equipment in that line, e.g., behind the welding station, it will be necessary to start the line and to take a sample from the first pipe passing through. Next, the dummy is made therefrom and only then will the ultrasonic test equipment be adjusted. Thus, an inherent extensive delay is incurred between this halted beginning and the resumption of production.
Another problem encountered is the weight of the dummy, again particularly when representing a large pipe. Handling of that dummy for purposes of equipment adjusted is greatly impeded by that weight. One needs cranes, vehicles, etc., just for moving the dummy into the desired positions. The sizes of the dummies pose the additional problem of storage.
Another problem relates to the aspect of reproducibility. Previous methods and procedures suffered because of inadequacy on that account. For example, reproducible positioning of the test equipment requires, for example, establishing of accurate and definable angles of incidence for the ultrasonic test beam into the object. Also, specific distances must be established.
It was found that "defects" in dummies do not permit adequate adjustment of that angle, agle, and equipment spacing can also be approximated only. The reason is that the equipment is positioned by an operator and is thus subjective. Also, similar test defects will exhibit different reflectivity in different dummies and objects because of differences in overall geometry as well as because of tolerances in generating the test defects.